The present invention relates to an oxide-ceramic target for cathode sputtering consisting of partially reduced indium oxide-tin oxide mixtures and to a method of producing these targets by means of hot-pressing.
Oxide-ceramic targets of indium oxide-tin oxide are used for producing transparent, electrically conductive, thin layers by means of cathode sputtering. Such layers are used in particular in liquid crystal display technology and in flat panel display technology. The thin layers of indium oxide-tin oxide can be produced either by sputtering metallic targets in an oxygen-reactive atmosphere or by means of sputtering oxide-ceramic targets. The sputtering process with oxide-ceramic targets has the advantage that the regulating of the sputtering process is simplified because the oxygen flow, or flux, in the sputtering chamber is only slight, compared to the high oxygen flows necessary when sputtering with metallic targets.
In order to achieve the lowest possible specific electrical resistances in the thin layer of indium oxide-tin oxide and to make high sputter performances possible, partially reduced indium oxide-tin oxide targets are preferably used.
The oxygen content is reduced in these targets in comparison to the stoichiometric oxides. These targets exhibit better electric and thermal conductivities and can be compressed to greater densities.
German OLS 33 00 525 teaches partially reduced indium oxide-tin oxide targets and their production. This document is entirely incorporated herein by reference. According to this publication, indium oxide-tin oxide powder mixtures are hot-pressed under reducing conditions at 850.degree. to 1000.degree. C.; the oxides are hot-pressed in a graphite hot-press mould or by means of the addition of carbon or organic material liberating carbon. The oxides are partially reduced during the hot-pressing procedure, so that a target is created that is depleted in its oxygen content in comparison to the stoichiometric composition.
A disadvantage of this method is the fact that a predeterminable precise maintenance of a certain oxygen stoichiometry can not be achieved on account of the reduction conditions during the pressing. Moreover, targets are obtained which exhibit, with a specific electric resistance of 0.1 to 0.6 .OMEGA. cm, a relatively poor electric conductivity, which is negative for the sputter performance which can be achieved.
EP patent 0,386,932 teaches a target of indium oxide-tin oxide which exhibits, as a consequence of a primary particle size of 0.01 to 1 .mu.m and a BET surface of the particles of 15 to 50 m.sup.2 /g, a density of more than 75% of the theoretical density and a specific electric resistance of 2.times.10.sup.-3 to 2.times.10.sup.-4 .OMEGA. cm. This document also is entirely incorporated herein by reference.
The process preferably takes place in air but can also occur in inert gas or in a vacuum. In the latter instances, a non-defined deficit of oxygen is obtained in the target material. No optimum sputter performances can be achieved with such targets.